Thiol-ene free radical chemistry is known from early works that are dated back to late 1930s. A review “Thiol-Enes: Chemistry of the Past with Promise for the Future” is written by Charles E. Hoyle, Tai Yeon Lee, Todd Roper in J. Polym. Sci. Part A: Polym. Chem.: Vol. 42 (2004). Thiolenes have been used in the following fields: clear protective coatings, pigmented coatings, photoinitiated liquid crystalline structural materials and adhesives.
Impregnation/modification of wood is described in many applications and patents. The main objective in these applications has been to prevent the wood from degradation and fungi by improving the water resistance. Focus for the last years has been to replace old impregnation methods with new, environmental friendly techniques. Several promising techniques are based on treating wood with furfuryl (WPT/Kebony), acetyl (Accoya/Accsys/Titanwood), phenol (Fibron, C-K composites, Permali etc) or urea/melanin/formaldehyde resin (BASF/Belmadur).
Water/aqueous based impregnation techniques depend largely on controlled swelling of the wood cells during an energy intensive process including high temperature and pressure over time. Several of the techniques show good performance with improved water resistance, but none have so far proved to be cost efficient. Common drawbacks are also limited penetration of the impregnation liquid, discolouring and to some extent swelling of the impregnated wood products.
Impregnation with organic oils like Tung and Linseed oil has historically been the preferred impregnation technique for wood. The oils depend on a slow air oxidation mechanism to cure properly. Penetration is limited, often resulting in an incomplete water resistance.
Wood is a preferred material for furniture productions. However, massive wood constructions have limited mechanical strength compared to materials like metal and various composite materials. Furniture designers are therefore forced to use other materials when thin constructions are required.
Further, rapid deforestation of tropical rain forest combined with a dramatic climate change have put focus on how to substitute dark coloured tropical wood in applications like flooring, furniture and boat decking. In several of the recent impregnation techniques mentioned earlier, the resulting wood is usually darkened and/or miscoloured. This side effect can be utilized in copying some tropical wood species by impregnating lighter/softer wood. This colouring is however hard to control with respect to exact copying the tropical appearance.
There is therefore a demand for improving the properties in wood products in several areas. Examples are water resistance, improved hardness, dimension stability, mechanical strength, stiffness and colourisation. Colourisation combined with increased mechanical strength will be a important area in the years to come. The objective will be to substitute rainforest wood in most applications to preserve a scarce and fragile resource.